The goal of this proposal is to develop novel methods for high-yield, low-cost production of high performance cerium-doped lutetium oxyorthosilicate (LSO) scintillating crystals. The motivation is that LSO is amongst the most promising new scintillators discovered in almost five decades, with a unique combination of important properties for x and gamma-ray spectroscopy, namely: high density, fast decay, and large light yield relative to BGO. LSO seems to be a prime candidate to replace BGO in PET systems. However, the practical utilization of LSO is hindered by difficulties related to crystal growth (Czocharalski method) due to the high temperatures employed. During the Phase I effort proposed we will perform a feasibility study to show that the innovative approach using a new low-temperature crystal growth technology can solve these problems. Specific tasks include preparation of lutetium precursors, and growth of both extremely fine grained (for optical transparency) polycrystalline LSO, and single crystal LSO via these new techniques. These samples will be thoroughly investigated for crystallinity, stochiometry and optical transparency. Scintillation properties and response to 500 keV gamma-rays will be measured and compared with bought crystals grown by the Czochralski method. In Phase II we will optimize the growth technique and streamline the process to obtain large volume, high performance and low cost LSO scintillating crystals specifically suited for PET detector rings. PROPOSED COMMERCIAL APPLICATION To date LSO is still not commercially available. When available its use will be widespread in hosts of applications leading to immediate performance gains, or enabling completely new uses where fast-timing or high counting-rate is needed. These include: PET,; high-energy physics; industrial process control; environmental monitoring; geophysics; and space instrumentation etc., as well as brand new uses with solid-state photodectectors such as APD s and new drift detectors.